Normally, electric motors used in windshield wipers of motor vehicles comprise a housing with a metallic housing case which is bent or rolled from a metal blank. Thereby as to some manufacturing methods the metal blank is bent around the bottom when rolling the housing case, whereby holding means on the bottom and holding means on the metal blank engage one after the other. Thus, when the metal blank is bent, the bottom of the motor housing is fixed at the same time. As to other manufacturing methods first of all the metal blank is bent in the shape of a pipe-like housing case and only in a subsequent operational step the housing bottom or housing lid is fixed onto this housing case.
Then in most of the windshield wiper motors the housing case is coated with a cover serving as protection against corrosion and ensuring, furthermore an improved radiation of heat. For this purpose in some cases, a black baking varnish is put on. In other cases the housing case is coated with a powder. In both cases heat has to be supplied in this operational step so that the cover is of the necessary hardness and constancy. As to the powder coating for example, first of all the housing is heated by hot air, then the material is put on and finally the housing is kept at higher temperature until the coating powder is hardened.
Then the magnets are fixed onto the housing provided with such a varnished or coated cover. For this purpose normally resilient clamps riveted with the housing case are used.
Already for reasons of tolerance the outer contour of the magnet cannot exactly be in accordance with the contour of inner surface of the housing case. Therefore the magnet is dimensioned in such a way that it lies only on those border areas on the inside of the housing case, on which it is held by the resilient clamps, whereby in the middle angle area of the segment-like magnet a gap towards the housing case remains. In most cases this gap is filled by a varnish put on afterwards. Thus unwanted noises caused by vibrations of the magnet which is resiliently supported shall be avoided.
Wiper motors manufactured according to this method have proved very worthwhile in practice to a large extent. However, it must be noted that assembling the magnets with riveted resilient clamps causes problems and that automatizing this operational step is only possible under great efforts. Besides, there are relatively big deviations of tolerance, and an unduely big number of noises caused by vibrations cannot totally be excluded despite the varnish filled into the gap.